Abstract
We derive vertical temperature profiles from Ion Neutral Mass Spectrometer (INMS) N2 density measurements from 32 Cassini passes. We find that the average temperature of Titan's thermosphere varies significantly from pass-to-pass between 112 and 175K. The temperatures from individual temperature profiles also varies considerably, with many passes exhibiting wave-like temperature perturbations and large temperature gradients. Wave-like temperature perturbations have wavelengths between 150 and 420km and amplitudes between 3% and 22% and vertical wave power spectra of the INMS data and HASI data have a slope between -2 and -3, which is consistent with vertically propagating atmospheric waves. The lack of a strong correlation between temperature and latitude, longitude, solar zenith angle, or local solar time indicates that the thermal structure of Titan's thermosphere is not primarily determined by the absorption of solar EUV flux. At N2 densities greater than 108cm-3, Titan's thermosphere is colder when Titan is observed in Saturn's magnetospheric lobes compared to Saturn's plasma sheet as proposed by Westlake et al. (Westlake, J.H. et al. [2011]. J. Geophys. Res. 116, A03318. http://dx.doi.org/10.1029/2010JA016251). This apparent correlation suggests that magnetospheric particle precipitation causes the temperature variability in Titan's thermosphere; however, at densities smaller than 108cm-3 the lobe passes are hotter than the plasma sheet passes and we find no correlation between the temperature of Titan's thermosphere and ionospheric signatures of enhanced particle precipitation, which suggests that the correlation is not indicative of a physical connection. The temperature of Titan's thermosphere also may have decreased by ~10K around mid-2007. Finally, we classify the vertical temperature profiles to show which passes are hot and cold and which passes have the largest temperature variations. In a companion paper (Part II), we estimate the strength of energy sources and sinks in Titan's thermosphere.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 552-582 |
| Number of pages | 31 |
| Journal | Icarus |
| Volume | 226 |
| Issue number | 1 |
| DOIs | |
| State | Published - Sep 2013 |
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Keywords
- Aeronomy
- Atmospheres, structure
- Titan, atmosphere
ASJC Scopus subject areas
- Space and Planetary Science
- Astronomy and Astrophysics
Cite this
The thermal structure of titan's upper atmosphere, I : Temperature profiles from Cassini INMS observations. / Snowden, D.; Yelle, Roger; Cui, J.; Wahlund, J. E.; Edberg, N. J T; Ågren, K.
In: Icarus, Vol. 226, No. 1, 09.2013, p. 552-582.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The thermal structure of titan's upper atmosphere, I
T2 - Temperature profiles from Cassini INMS observations
AU - Snowden, D.
AU - Yelle, Roger
AU - Cui, J.
AU - Wahlund, J. E.
AU - Edberg, N. J T
AU - Ågren, K.
PY - 2013/9
Y1 - 2013/9
N2 - We derive vertical temperature profiles from Ion Neutral Mass Spectrometer (INMS) N2 density measurements from 32 Cassini passes. We find that the average temperature of Titan's thermosphere varies significantly from pass-to-pass between 112 and 175K. The temperatures from individual temperature profiles also varies considerably, with many passes exhibiting wave-like temperature perturbations and large temperature gradients. Wave-like temperature perturbations have wavelengths between 150 and 420km and amplitudes between 3% and 22% and vertical wave power spectra of the INMS data and HASI data have a slope between -2 and -3, which is consistent with vertically propagating atmospheric waves. The lack of a strong correlation between temperature and latitude, longitude, solar zenith angle, or local solar time indicates that the thermal structure of Titan's thermosphere is not primarily determined by the absorption of solar EUV flux. At N2 densities greater than 108cm-3, Titan's thermosphere is colder when Titan is observed in Saturn's magnetospheric lobes compared to Saturn's plasma sheet as proposed by Westlake et al. (Westlake, J.H. et al. [2011]. J. Geophys. Res. 116, A03318. http://dx.doi.org/10.1029/2010JA016251). This apparent correlation suggests that magnetospheric particle precipitation causes the temperature variability in Titan's thermosphere; however, at densities smaller than 108cm-3 the lobe passes are hotter than the plasma sheet passes and we find no correlation between the temperature of Titan's thermosphere and ionospheric signatures of enhanced particle precipitation, which suggests that the correlation is not indicative of a physical connection. The temperature of Titan's thermosphere also may have decreased by ~10K around mid-2007. Finally, we classify the vertical temperature profiles to show which passes are hot and cold and which passes have the largest temperature variations. In a companion paper (Part II), we estimate the strength of energy sources and sinks in Titan's thermosphere.
AB - We derive vertical temperature profiles from Ion Neutral Mass Spectrometer (INMS) N2 density measurements from 32 Cassini passes. We find that the average temperature of Titan's thermosphere varies significantly from pass-to-pass between 112 and 175K. The temperatures from individual temperature profiles also varies considerably, with many passes exhibiting wave-like temperature perturbations and large temperature gradients. Wave-like temperature perturbations have wavelengths between 150 and 420km and amplitudes between 3% and 22% and vertical wave power spectra of the INMS data and HASI data have a slope between -2 and -3, which is consistent with vertically propagating atmospheric waves. The lack of a strong correlation between temperature and latitude, longitude, solar zenith angle, or local solar time indicates that the thermal structure of Titan's thermosphere is not primarily determined by the absorption of solar EUV flux. At N2 densities greater than 108cm-3, Titan's thermosphere is colder when Titan is observed in Saturn's magnetospheric lobes compared to Saturn's plasma sheet as proposed by Westlake et al. (Westlake, J.H. et al. [2011]. J. Geophys. Res. 116, A03318. http://dx.doi.org/10.1029/2010JA016251). This apparent correlation suggests that magnetospheric particle precipitation causes the temperature variability in Titan's thermosphere; however, at densities smaller than 108cm-3 the lobe passes are hotter than the plasma sheet passes and we find no correlation between the temperature of Titan's thermosphere and ionospheric signatures of enhanced particle precipitation, which suggests that the correlation is not indicative of a physical connection. The temperature of Titan's thermosphere also may have decreased by ~10K around mid-2007. Finally, we classify the vertical temperature profiles to show which passes are hot and cold and which passes have the largest temperature variations. In a companion paper (Part II), we estimate the strength of energy sources and sinks in Titan's thermosphere.
KW - Aeronomy
KW - Atmospheres, structure
KW - Titan, atmosphere
UR - http://www.scopus.com/inward/record.url?scp=84879549230&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84879549230&partnerID=8YFLogxK
U2 - 10.1016/j.icarus.2013.06.006
DO - 10.1016/j.icarus.2013.06.006
M3 - Article
AN - SCOPUS:84879549230
VL - 226
SP - 552
EP - 582
JO - Icarus
JF - Icarus
SN - 0019-1035
IS - 1
ER -